The present invention relates to a toner used for electrophotographic reproduction.
Image formation by electrophotography is widely known. In the general method, photosensitive member is entirely charged by corona discharge, then an electrostatic latent image is created by illumination of the image. In this case, exposed portion of the photosensitive member may become conductive, losing charge, and unexposed portion remains as an electrostatic latent image. When toner having reversed polarity is brought close to the electrostatic latent image, the toner is electrostatically attracted and the latent image is made visible and developed. Such image is usually transferred to paper in xerography or directly fixed on a photosensitive member in electrofax process.
The conventional image formation processes above mentioned involves complicated steps and requires a complex and expensive electrophotographic copying machine. Further, since the copy system comprises independent members, that is, a photosensitive member and toner powder, i.e., developer, deterioration of either of the above two members, for example, fatigue of the photosensitive member by illumination or deterioration of charge properties of the developer, results in difficulty in obtaining high definition copy. Therefore, the desired properties of the photosensitive member and the developer should be always maintained. Thus, troublesome maintenance of system is required.
Recently, a duplication process, wherein a photosensitive member is substituted by a photoconductive toner which is obtained by imparting photoconductivity to a developer, has been proposed to solve the foregoing problems.
Since the duplication process using photoconductive toner is a process wherein formation ability of electrostatic latent image is imparted to toner itself and a photosensitive member is not required, electrophotographic copying machine may be simplified, which advantageously results in decreased cost of product. Moreover, in this process, full-color image may be produced by one-shot.
Development of the photoconductive toner comprises formation of thin layer of toner onto a conductive substrate, followed by electrification, exposure, image transfer and fixing (see, for example, U.S. Pat. No. 2,758,939).
In development step of the photoconductive toner, it is required to form the thinnest, most uniform and largest-area toner layer on the photoconductive substrate from the viewpoint of enhancement of photosensitivity. The photoconductive toner hardly possesses practical photosensitivity partly because it is extremely difficult to satisfy such requirement. It is partly attributable to the problems such as ununiform triboelectrification and dusting of toner. Such deficient charge and dusting result in disarrangement or fog in duplicated image to deteriorate the picture qualities.
To solve above problems, magnetic material is proposed to be incorporated in toner (see, Japanese Patent Laid Open Publication No. 177157/1982 etc.).
However, all magnetic materials proposed in the above disclosure are inorganic and accompanied with problems of compatibility and dispersibility in resin. However, all magnetic materials proposed in the above disclosure are inorganic. The use of inorganic magnetic powder is accompanied with significant adverse effect. That is, inorganic magnetic powder itself does not have transparency. Further, it is difficult to uniformly disperse and incorporate inorganic magnetic powder in resin, resulting in muddiness as well as marked deterioration of transparency. Therefore, insufficient transparency of toner inevitably causes deterioration of photosensitivity. There is also a problem of muddiness in color images, so transparency of toner is insufficient and deterioration of photosensitivity is inevitable. There is also a problem of muddiness in color images.